“Determination of the point-spread function of human eyes using a hybrid optical-digital method”, J. Opt. Soc. Am. A, 4, 1109-1114 (1987) by J. Santamaría, P. Artal, J. Bescós describes the mentioned double-pass technique based on projecting a point light beam on the retina of the patient and directly recording the light reflected from it following the double passage of the light through the ocular means which allows obtaining the objective measurement of aberration and scattering contributions to ocular optical quality (F. Díaz-Doutón, A. Benito, J. Pujol, M. Arjona, J. L. Güell, P. Artal, “Comparison of the retinal image quality obtained with a Hartmann-Shack sensor and a double-pass instrument”, Inv. Ophthal. Vis. Sci., 47, 1710-1716 (2006)).
The in vitro evaluation of the optical quality of multifocal intraocular lenses or contact lenses can be carried out using single-pass systems consisting of forming the image of an object on a CCD camera before the passage of the light through the multifocal means (Artigas J. M, Menezo J. L, Penis C, Felipe A., Diaz-Llopis M., “Image quality with multifocal intraocular lenses and the effect of pupil size”, J Cataract Refract Surg 2007; 33:2111-2117 2007, Pieh S., Fiala W, Malz A, Stork W., “In Vitro Strehl Ratios with Spherical, Aberration-Free, Average, and Customized Spherical Aberration-Correcting Intraocular lenses” Invest. Ophthalmol. Vis. Science 50 1264-1270 (2009), Maxwell W. A., Lane S. S., Zhou F., “Performance of presbyopia-correcting intraocular lenses in distance optical bench tests” J Cataract Refract Surg 2009; 35:166-171). To take these measurements it is necessary to use an artificial eye where the multifocal system can be placed. The ISO 11979-2 [ISO 00] standard is available today providing the guidelines on how this eye should be and what conditions must be met to enable taking the measurement.
Double-pass technique with a conventional design in which the focus corrector is the same in the first and second passage has been used for evaluating the optical quality in multifocal intraocular lenses and contact lenses (Pujol, J.; Gispets, J.; Arjona, M. “Optical performance in eyes wearing two multifocal contact lens designs”. Ophthalmic Physiol Opt., 2003, vol. 23, no. 4, p. 347-60, Gispets, J.; Arjona, M.; Pujol, J. “Image quality in wearers of a centre distance concentric design bifocal contact lens”. Ophthalmic Physiol Opt., 2002, vol. 22, no. 3, p. 221-33, P. Artal, S. Marcos, R. Navarro, I. Miranda, and M. Ferro, “Through focus image quality of eyes implanted with monofocal and multifocal intraocular lenses” Opt. Eng. 34, 772-779 (1995), Fernández-Vega L, Madrid-Costa D., Alfonso J. F., Montés-Micó R., Poo-López A., “Optical and visual performance of diffractive infraocular lens implantation after myopic laser in situ keratomileusis” J Cataract Refract Surg 2009; 35:825-832, Castillo-Gómez A, Carmona-González D., Martinez-de-la-Casa J. M., Palomino-Bautista C, Garcia-Feijoo J., “Evaluation of image quality after implantation of 2 diffractive multifocal intraocular lens models” J Cataract Refract Surg 2009; 35:1244-1250). This technique can be used for taking measurements in vivo and in vitro, nevertheless it has a very significant limitation. In the first passage, upon forming the image of a point object on the retina, it will only be focused on a position of the focus corrector (generally the one corresponding to far vision), and upon introducing any other defocus for evaluating other vision conditions (near vision for example) this image will be defocused on the retina of the patient and therefore the image recorded on the camera in the second passage will be affected by the defocus occurring in the first passage.
The measurement of the ocular aberrations has also been used for characterizing the optical quality of multifocal intraocular lenses or contact lenses (Jeong, T. M.; Menon, M.; Yoon, G. “Measurement of wave-front aberration in the soft contact lenses by use of a Shack-Hartmann wave-front sensor”. Applied Optics, 2005, vol. 44, no. 21, p. 4423-7, Martin, J. A.; Roorda, A. “Predicting and assessing visual performance with multizone bifocal contact lenses”, Optom. Vis. Sci., 2003, vol. 80, no. 12, p. 812-19, Peyre, C.; Fumery, L.; Gatinel, D. “Comparison of high-order optical aberrations induced by different multifocal contact lens geometries”. J Fr Ophtalmol., 2005, vol. 28, no. 6, p. 599-604). This technique also has significant limitations. On one hand, depending on the configuration of the sensor used for measuring ocular aberrations, it may have the same limitation as the conventional double-pass technique due to the defocus of the image of a point object on the retina formed in the first passage of the light through the eye. Another limitation of all these sensors is due to the difficulty in measuring the aberrations in discontinuous optical areas such as those found in multifocal intraocular lenses or contact lenses, particularly those having a refractive design. In fact, this difficulty or impossibility have been shown clearly in different published works (Charman W. N, Montés-Micó R., Radhakrishnan H., “Problems in the Measurement of Wavefront Aberration for Eyes Implanted With Diffractive Bifocal and Multifocal Intraocular lenses”, Journal of Refractive Surgery Volume 24 March 2008, Jendritza B. B., Knorz M. C, Morton S., “Wavefront-guided Excimer Laser Vision Correction After Multifocal IOL Implantation”, Journal of Refractive Surgery Volume 24 March 2008).
By analyzing the quality of images obtained for different defocuses, it is possible to determine the range in which the patient can see the images sharply enough, corresponding to the pseudo-accommodation range. Application WO2009133224 belonging to two of the present inventors describes a method and a system for the objective measurement of ocular accommodation wherein the mentioned double-pass technique is also used for its implementation.